I'm talking about a neutral hydrogen atom here:
- According to Bohr, if the electron jumps from $n=2$ to $n=1$, there'd be only one wavelength of light being emitted. However, that is not the case we see experimentally. When an electron jumps from $n=1$ to $n=2$, more than one frequency of light, the values of which will be very close to each other (say $500nm$ and $500.01nm$) can be emitted. This is because, in the same shell, there are subshells, and some subshells have more energy than others. So, if the electron jumps from the $2s$ subshell to the $1s$ subshell, the emitted light's wavelength will be say $500.01nm$, and if the electron jumps from $2p$ to $1s$ the emitted light's wavelength will be say $500nm$. This is because the energy difference between $1s$ and $2s$ and $1s$ and $2p$ aren't the same. So, when an electron jumps from $n=2$ to $n=1$, there won't be a single line in the emission spectra as predicted by Bohr, rather there will be multiple fine lines very close to each other.
- Bohr's model can't explain the splitting of spectral lines into multiple fine lines under the influence of an electric or magnetic field. The spectral lines split because within subshells, there are orbitals, and they are differently oriented three-dimensionally. This has significant electromagnetic implications. For example, a $p$-subshell has three orbitals $p_x,p_y$ & $p_z$. They are differently oriented three-dimensionally, and as they have electrons moving in them, they have different electromagnetic orientations as well even though their energies are the same: they are degenerate orbitals. So, normally, in an emission spectrum, you don't notice any difference between $p_x,p_y$ & $p_z$ as they have the same energy, but under the influence of an electric or a magnetic field, you start to appreciate their individuality, as the lines emitted split. I think when observing the fine line of a $p$-subshell, if we apply an electric or a magnetic field, the line of the $p$-subshell will split into three finer lines with the same wavelength.
- Is my explanation as a whole correct?
PS: In reality, there are no such things as shells or subshells. There are only orbitals. To make the learning curve less steep, teachers use these terms to high-school students like us.